Reversible coupling of 4-nitroaniline molecules to 4-aminothiophenol functionalized on Ag nanoparticle/graphene oxide nanocomposites through the plasmon assisted chemical reaction

In this study, we demonstrate the formation of azo compounds on a composite of silver nanoparticles and graphene oxides (Ag@G) through a plasmon-assisted coupling reaction between different amine compounds. According to the time-dependent SERS experiments, 4-aminothiophenol (4ATP) molecules on Ag@G can be associated with external reactants such as 4-nitroaniline to form azo compounds when aided by the plasmons. Furthermore, the rate of the coupling reaction is dependent on the wavelength and the power of the excitation laser. It is noteworthy that the coupling reaction can only occur between two compounds containing amino groups in the presence of Ag nanoparticles. On the other hand, the NN double bond in the azo compound can be dissociated in a NaBH4 solution after 532 nm laser irradiation. The reduction of the azo compound results in the recovery of 4ATP molecules on Ag@G. Finally, we demonstrate that the plasmon-assisted coupling reaction allows for the immobilization of amine-terminated DNAs on 4ATP modified Ag@G. This DNA modified Ag@G can serve as the SERS substrate to sensitively detect its complementary DNA.